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Let's Talk About CPTu

Cone penetration testing or CPT is an in-situ ground investigation technique. First developed in the 1930s as a mechanical device, the aim of this device was to determine the soil stratigraphy. The mechanical device was replaced with an electrical probe in the 1960s allowing the user to continuously measure the soil properties. Since the 1970s, many useful additions were made to the electrical cone to further improve in-situ investigations. One of the most significant additions to the electrical probe was the addition of a porewater pressure (PWP) transducer, now more commonly referred to as Piezocone penetration testing or CPTu. The ability to measure PWP has greatly improved the accuracy in determining the geotechnical properties of soils. CPTu can also measure the static PWP by performing dissipation tests at any given depth to determine the location of the phreatic surface. 

CPTu tests are executed by pushing the piezocone into the soil at a constant rate of 2cm/sec. To reach the required depths, one-metre rods are added as the hole progresses. Test observations and parameters such as; cone tip resistance (qc), local sleeve friction (fs), dynamic pore water pressure (u2), inclination and temperatures are recorded, in cm intervals, on a Pagani Geotechnical computer. CPTu tests are considered complete once the client’s specified depths are reached or in the case of refusal. 

GeoGroup prides itself on providing reliable and accurate data. The raw data obtained during the field tests are thoroughly checked by numerous parties within GeoGroup for any data anomalies. It is then imported into the CPeT-IT software developed by GeoLogismiki, one of the leading software brands in the world of CPT analysis. Further data quality checks are done with the aid of the software. A comprehensive CPT report is then compiled and submitted to the client as per their request.

GeoGroup has four CPT rigs with another one in the manufacturing process. The fleet consists of:
  • The Pagani TG73-200 offers static and dynamic penetrometer tests in a single rig. It can be configured to perform CPT, SPT and DPSH tests. The TG73-200 has been used on tailings facilities, river barges and many other hard to reach places.
  • The Pagani TG63-150 is a smaller, easily transportable, more manoeuvrable static CPT rig for easy testing in difficult locations such as tailings facilities.
  • The 16-ton Colossal CPT-150 is a customized CPTu rig, specially designed with stability in mind. With a Pagani CPT 150 mast fitted to a Morooka track-based carrier, the rig is ideal for conducting CPTu tests where the ground conditions show characteristics of a lower shear strength value or cohesiveness.
  • A Pagani 150kN hydraulic push cylinder mounted on the bed of a truck which is currently being assembled by the GeoGroup workshop team.